The invention relates to calenders and super calenders of the type used to finish paper for printing or other applications where a relatively high smoothness is required. In such devices the paper passes between the nip of a number of rollers and by the circumferential friction of the rolls on the paper surface a polishing action is obtained. The rollers are generally arranged in a vertical stack. Iron rolls alternate with paper filled rolls, that is, rolls which are formed by placing a large number of doughnut-like paper disks on a common shaft. These paper filled rolls are largely responsible for the polishing action.
Paper filled rolls are easily damaged in the event that there is a break in the paper web being polished. When the web breaks it bunches and jams between the nips of the rollers causing unevenness on the surface of the paper filled rolls impairing the ability of such rolls to polish the web evenly.
In an effort to avoid damage to paper filled rolls when a web breaks and to permit adjustment of the spacing between rolls as they wear down, it is necessary to provide some mechanism for positioning the rolls relative to each other and for rapidly separating them in the event of a break in the paper web or similar emergency condition which could damage the rolls. Separating systems are known in the prior art and, for example, see U.S. Pat. Nos. 3,777,656, 3,948,166, and 3,584,570 which disclose lifting mechanisms. These references are discussed more fully in the Prior Art Statement submitted with this application and hereby incorporated by reference. Although lifting mechanisms are known, none of the foregoing has the capability of rapidly separating the rolls in the event of an emergency condition and the capability of automatically repositioning the rolls to their correct operative positions particularly when a worn paper roll has been replaced with a new roll of a different diameter.
U.S. Pat. No. 4,266,475, assigned to the present assignee, discloses a positioning mechanism which is capable of rapidly separating calender rolls in the event of an emergency condition and automatically repositioning the rolls to resume operation. That patent discloses a system suitable for a two column calender machine and employs a lost motion connection between the rod eye of the piston and the pin used for securing it to the flange plate of the cylinder immediately thereabove. The present invention constitutes an improvement upon the construction disclosed in the '475 patent and is suitable for applications where the device of the '475 patent could not be employed.
The present invention is a four column design in which each roll is supported for vertical movement on the four columns. Four rather than two piston and cylinder assemblies are associated with each roll and a lost motion connection is provided between a side plate and the bearing housings associated with each roll. Such construction has several advantages: larger calender machines can be built due to the added strength of the four column design; it is as quick as or quicker than the two column design in separating the rolls; it is sturdier and has more tolerance to vibration than the two column design and, significantly, most existing calender equipment employs a four column support system.
The present invention thus permits existing equipment to be retrofitted to obtain the advantages of the present invention with minimum down time. The device of the '475 patent, although suitable for new calender machines, is not easily retrofitted to existing calender machines.
It is accordingly an object of the invention to provide an improved positioning mechanism for four column calender machines which is capable of accomplishing rapid separation of the rolls in an emergency situation.
A further object of the invention is to provide a device of the type described capable of automatically repositioning the rolls in their proper operative relation regardless of changes in the roll diameter of the rolls in the calender stack.
A further object of the invention is to provide a hydraulic cylinder lifting mechanism for a four column calender machine which utilizes an improved lost motion connection to rapidly space the rolls one from the other in an emergency situation by an amount determined by the lost motion elements.
A further object of the invention is to provide a hydraulic lowering mechanism for a calender stack which can rapidly separate the rolls in the stack by a preset amount to limit damage to the rolls in the event of a paper break.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.